1. Field of the Invention
The present invention relates to an optical data recording apparatus which records data on an optical data recording medium, such as on an optical disk.
2. Description of the Related Art
According to such an apparatus, a light beam with a predetermined intensity irradiates a writable or erasable optical disk to record data thereon. The most serious problem for this type of apparatus is the overwriting of new data on those tracks which have data already recorded thereon. The main cause for such overwriting is improper tracking at the time of data recording.
A conventional measure to prevent overwriting is disclosed in Japanese Patent Disclosure No. 54-147006. The disclosed conventional apparatus has a circuit for searching for a non-recorded region while monitoring a reproduced signal at the time of data recording, and a gate for disabling a recording circuit even upon reception of a recording command unless a non-recorded region detection signal is present. Another apparatus, known in the art, writes a record-completion flag in a recorded region on the recording medium to thereby prevent overwriting (data destruction).
However, these conventional apparatuses for preventing overwriting are not particularly designed to cope with a case where data on an optical disk is destroyed by malfunction of a circuit itself for controlling light emission of a semiconductor laser. At the time of data recording or reproducing with a light emission command being issued, if only a laser beam with a less than a predetermined intensity is detected due to malfunction of a photodiode, a laser may emit a high intensity of light because of a feedback control employed so that data is erroneously written on the recording medium. The aforementioned data destruction preventing measures cannot deal with this case; no precautions taken against such abnormal light emission would certainly increase and spread data destruction.